Electrotherapy is therapy where electricity is applied to the body for medical purposes. One application of electrotherapy is where electrical stimulation is applied to the nervous system to improve neurological or psychiatric conditions. When electrical stimulation is applied though electrodes on the surface of the body, for example the scalp, it is non-invasive. In some systems, a minimum of two electrodes are required, but some systems utilize more electrodes to enhance targeting of brain regions. The waveform of stimulation describes the temporal pattern applied to the electrodes. The waveform of stimulation as applied to two or more electrodes determines the therapeutic actions.